Definition
ROAS, or return on ad spend, is the revenue generated for every unit of currency spent on advertising. It is the headline efficiency metric for paid acquisition: a ROAS of 4 means you earned four dollars in revenue for each dollar of ad spend.
ROAS is easy to calculate and easy to misread. It measures revenue efficiency, not profit, so a campaign can post a strong ROAS and still lose money once product cost, shipping and fees are counted.
How to calculate ROAS
The formula is:
ROAS = Revenue from ads ÷ Ad spend
For example, 40,000 dollars of revenue from 10,000 dollars of ad spend is a ROAS of 4, often written 4:1. Its inverse, ACOS (advertising cost of sale), is ad spend divided by revenue, so a 4:1 ROAS is a 25% ACOS. You can work through both, plus gross ad profit, with the ROAS calculator.
Why ROAS matters, and its limits
ROAS tells you whether an ad channel is turning spend into revenue, which is essential for allocating budget. But the number that decides whether that spend is worth making is your break-even ROAS, and that depends entirely on your gross margin. If your margin is 40%, you need a ROAS above 2.5:1 just to cover the cost of goods, before overhead. A 3:1 ROAS is excellent for one store and a loss for another.
This is why ROAS should be read alongside profit, not on its own. A channel with a high ROAS on discount-driven, low-margin orders can quietly lose money, while a lower-ROAS channel that acquires loyal, high-margin customers can be your best. Turn attributed revenue into a profit view with the ecommerce profit calculator.
Read ROAS per campaign or channel, not only as a blended figure, because a healthy overall number can hide an individual channel that is losing money. ROAS also depends on attribution: the model decides which sales get credited to which ads, and models are assumptions rather than proof. Our guide to revenue attribution covers how to read and validate the revenue behind a ROAS figure, and why a large budget decision should be checked with an incrementality test rather than a reported ROAS alone.
Related metrics
ROAS pairs with gross margin, which sets your break-even point, and with customer lifetime value, because a channel that looks weak on first-order ROAS can be strong once repeat purchases are counted. Read together, they turn a raw efficiency ratio into a decision about profitable growth.
In short
ROAS is ad revenue divided by ad spend. It measures revenue efficiency, not profit, so it must be read against your margin and break-even, and validated with attribution and incrementality. A high ROAS is only good if the underlying orders are actually profitable.